Image forming apparatus

ABSTRACT

An image forming apparatus includes a transport unit that transports a recording medium along a transport path to a formation area in which an image is formed on the recording medium, an image forming unit that forms the image on the recording medium in the formation area, and a protrusion amount setting unit that sets a protrusion amount of the image protruding from the recording medium to a first protrusion amount in a first case, and sets the protrusion amount to a second protrusion amount larger than the first protrusion amount in a second case where the recording medium is inclined to a transport direction more than the first case.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 fromJapanese Patent Application No. 2019-039194 filed Mar. 5, 2019.

BACKGROUND (i) Technical Field

The present invention relates to an image forming apparatus.

(ii) Related Art

In the related art, in order to perform so-called borderless printing, atechnique is known which prints an image larger than the size of a sheetso as to be projected from the sheet.

In such borderless printing, in a case where the protrusion amount ofthe image protruding from the sheet is large, the sheet falls within theimage even in a case where the position of the sheet is shifted, so theborder of the sheet is prevented from being white out.

On the other hand, in a case where the protrusion amount is large, theuseless image portion not placed on the sheet is large, so theconsumption amount and the recovery amount of the ink and toner formingthe image are large, which is not desirable from the viewpoint of costand life.

Therefore, an image forming apparatus capable of adjusting theprotrusion amount has been proposed.

For example, JP2004-104190A discloses an apparatus which causes the userto set a protrusion amount corresponding to the size of an image whichprotrudes from the recording sheet and is not recorded due toenlargement of an original image, in a case where the original image isrecorded on a recording sheet in a borderless copy mode, and determinesa magnification for the enlargement, based on the protrusion amount setby a user.

Further, JP2006-220991A discloses an apparatus that controls theprotrusion amount of a plurality of toner images, based on the detectionresult of a passage detection unit that detects the passage of theleading edge position or the trailing end position of the recordingmaterial, in a case of performing borderless printing.

Further, JP4708668B discloses an apparatus which can designate one of aplurality of protrusion levels representing the protrusion amount,according to the user's instruction, and sets a combination of theprotrusion amount from each end which is associated in advance with theprotrusion level, according to the designated protrusion level.

SUMMARY

However, in the apparatus in the related art, a phenomena in which whitespots occur near the corners of the recording medium due to a so-calledskew, that is, a recording medium represented by a sheet is inclined tothe transport direction has not been considered, and setting of aprotrusion amount corresponding to the skew has not been proposed.

Aspects of non-limiting embodiments of the present disclosure relate toan image forming apparatus capable of setting an appropriate protrusionamount even in a case where a skew occurs.

Aspects of certain non-limiting embodiments of the present disclosureovercome the above disadvantages and/or other disadvantages notdescribed above. However, aspects of the non-limiting embodiments arenot required to overcome the disadvantages described above, and aspectsof the non-limiting embodiments of the present disclosure may notovercome any of the disadvantages described above.

According to an aspect of the present disclosure, there is provided animage forming apparatus including:

a transport unit that transports a recording medium along a transportpath to a formation area in which an image is formed on the recordingmedium;

an image forming unit that forms the image on the recording medium inthe formation area; and

a protrusion amount setting unit that sets a protrusion amount of theimage protruding from the recording medium to a first protrusion amountin a first case, and sets the protrusion amount to a second protrusionamount larger than the first protrusion amount in a second case wherethe recording medium is inclined to a transport direction more than thefirst case.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiment(s) of the present invention will be described indetail based on the following figures, wherein:

FIG. 1 is a schematic configuration diagram showing a first exemplaryembodiment of an image forming apparatus;

FIG. 2 is an explanatory view of borderless printing;

FIG. 3 is a view showing a sheet tray storing cut sheets;

FIG. 4 is a view showing a state of occurrence of a skew;

FIG. 5 is a view showing a state of occurrence of a skew in a cut sheethaving a rounded corner shape;

FIG. 6 is a view showing a state in which a cut sheet has reached aregistration roll;

FIG. 7 is an explanatory view for explaining skew correction;

FIG. 8 is an explanatory view for explaining skew correction in a narrowcut sheet;

FIG. 9 is an explanatory view for explaining skew correction in a cutsheet having a rounded corner shape;

FIG. 10 is a view showing bending of a cut sheet;

FIG. 11 is a view showing bending in a thick cut sheet;

FIG. 12 is a view showing a tray setting screen on which information oncut sheets is input;

FIG. 13 is a flowchart showing control for selectively using theprotrusion amount;

FIG. 14 is a view showing a measurement mechanism of the size of a cutsheet in a second exemplary embodiment;

FIG. 15 is a view showing a measurement mechanism of a skew amount in athird exemplary embodiment;

FIG. 16 is a view showing a method of measuring the skew amount of a cutsheet P from a detection value of a side edge sensor;

FIG. 17 is a view showing a measurement mechanism of a skew amount in afourth exemplary embodiment;

FIG. 18 is a view showing a method of measuring the skew amount of thecut sheet P from a detection value of a passage sensor;

FIG. 19 is a view showing a measurement mechanism of the shape of a cutsheet in a fifth exemplary embodiment;

FIG. 20 is a view showing a measurement example of a cut sheet having arounded corner shape in the fifth exemplary embodiment; and

FIG. 21 is a view showing a measurement mechanism of the thickness of acut sheet in a sixth exemplary embodiment.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram showing a first exemplaryembodiment of an image forming apparatus.

The image forming apparatus 100 shown in FIG. 1 is a so-called tandemtype color printer, and in the image forming apparatus 100, a cut sheetP is used as a recording material. In addition to the cut sheet P,plastic sheet and an envelope may be adopted as the recording material,but in the following description, the cut sheet P will be described as arepresentative of the recording material.

The cut sheets P are stored in a stacked state on a sheet tray 130provided at the lower part of the image forming apparatus 100. The cutsheets P in the sheet tray 130 are taken out one by one from the sheettray 130 by the feed roll 131 and the separating roll 132 andtransported upward along the transport path R.

In the case of the present exemplary embodiment, sheet trays 130 of twostages are provided. The sheet trays 130 may store cut sheets P ofdifferent sizes, respectively. Further, shapes of the cut sheet P thatcan be stored in the sheet tray 130 include a rounded corner shape inwhich the corners are cut, in addition to a normal shape in which thecorners are cut at right angles. Of the sheet trays 130 of two stages,the cut sheet P of the sheet tray 130 selected by the user is used forimage formation.

The image forming apparatus 100 is provided with, for example, fourimage engines 110Y, 110M, 110C, 110K corresponding to four colors ofyellow (Y), magenta (M), cyan (C), black (K). Further, in the presentexemplary embodiment, each of the image engines 110Y, . . . , 110K formsa toner image by a so-called electrophotographic method. In each of theimage engines 110Y, . . . , 110K, a toner image of each color is formedon each photoconductive drum by sequentially passing through the stepsof charging, exposure, and development. In the present exemplaryembodiment, the exposure step is performed by the exposure light emittedfrom one exposure apparatus 112 common to the four image engines 110Y, .. . , 110K.

In the image forming apparatus 100 of the present exemplary embodiment,a direct transfer method is adopted, and a sheet transport belt 120 isprovided. The sheet transport belt 120 is wound around a driving roll121 and a driven roll 122, and is circulated by the driving force of thedriving roll 121 through the respective image engines 110Y, . . . ,110K. At a position facing the driven roll 122 with the sheet transportbelt 120 interposed therebetween, an auxiliary roll 123 for assistingthe transport of the cut sheet P by the sheet transport belt 120 isprovided. The combination of the sheet transport belt 120 and the feedroll 131 corresponds to an example of the transport unit in the presentinvention.

Transfer rolls 111Y, 111M, 111C, 111K are disposed at respectivepositions facing the image engines 110Y, . . . , 110K with the sheettransport belt 120 interposed therebetween. After the cut sheets P takenout from the sheet tray 130 and transported along the transport path Rpass through the registration roll 135, the cut sheets P are transportedby the sheet transport belt 120, and pass between the image engines110Y, . . . , 110K and the transfer rolls 111Y, . . . , 111K. The tonerimages of the respective colors formed by the respective image engines110Y, 110K are sequentially superimposed and transferred onto the cutsheet P by the respective transfer rolls 111Y, 111K. As a result of suchtransfer, a color image is formed on the cut sheet P. The registrationroll 135 temporarily stops the cut sheet P, and sends the cut sheet P tothe sheet transport belt 120 at the same timing as image formation bythe image engines 110Y, . . . , 110K.

A combination of the image engine and the transfer roll corresponds toan example of the image forming device according to the exemplaryembodiment of the present invention, and an area between the imageengine 110Y, 110K and the transfer roll 111Y, . . . , 111K correspondsto an example of the formation area in the present invention.

The image forming apparatus 100 is provided with a fixing device 150,and the color image on the cut sheet P is fixed by heat and pressure bythe fixing device 150. The cut sheet P on which the image is fixed bythe fixing device 150 is sent out by the delivery roll 133 to thestacking tray 140 on the housing.

On the upper surface of the image forming apparatus 100, a display panel160 is provided which is responsible for inputting information andinstructions to the image forming apparatus 100 by the user, anddisplaying information from the image forming apparatus 100 to the user.

The image forming apparatus 100 further includes a cleaner 170 forscraping unnecessary things such as toner and sheet dust from the sheettransport belt 120 with a blade, and a control unit 180 that controlseach unit in the image forming apparatus 100.

The image forming apparatus 100 of the present exemplary embodiment isprovided with a so-called borderless printing function of forming animage on the entire surface of the cut sheet P. This borderless printingis realized by forming a toner image of a size exceeding the size of thecut sheet P by the image engines 110Y, . . . , 110K.

FIG. 2 is an explanatory view of borderless printing.

In the borderless printing at the normal time (A), the range of the cutsheet P fits in the range of the toner image 200, so an image is formedon the entire surface of the cut sheet P. Hereinafter, the width of theportion where the range of the toner image 200 exceeds the range of thecut sheet P will be referred to as a protrusion amount 210. As theprotrusion amount 210, different amounts in the vertical direction andthe horizontal direction of the cut sheet P may be adopted, but for thesake of simplicity of description, the cut sheet P will be describedbelow as having the identical protrusion amount 210 in the verticaldirection and the horizontal direction. The protrusion amount 210 at thenormal time (A) is, for example, 2 mm.

In a case where the cut sheet P is taken out of the sheet tray 130 andtravels along the transport path R, a so-called skew may occur in thetransport direction. At the skew time (B), as shown by the arrows inFIG. 2, the corner portions of the cut sheet P are displaced to theoutside than at the normal time (A). In a case where the skew is small,the positional deviation of the corner portion is small, so the entiresurface of the cut sheet P falls within the range of the toner image200. However, in a case where the skew is large, a whiteout area 220that protrudes beyond the range of the toner image 200 at the cornerportion of the cut sheet P. At the countermeasure time (C) forpreventing the occurrence of such a whiteout area 220, a protrusionamount 230 wider than that at the normal time (A) is used. Theprotrusion amount 230 at the countermeasure time (C) is, for example, 3mm. However, such a wide protrusion amount 230 causes an increase intoner consumption amount. Further, the toner of the toner image 200which has exceeded the range of the cut sheet P is scraped off by thecleaner 170 from above the sheet transport belt 120 and is collected bya collection mechanism (not shown). The wide protrusion amount 230causes an increase in the amount of collected toner and shortens thelife of the apparatus. Therefore, the protrusion amount 210 at thenormal time (A) and the protrusion amount 230 at the countermeasure time(C) can be selectively used according to the magnitude of the skew.

Here, the occurrence and correction of skew will be described.

FIG. 3 is a view showing a sheet tray storing cut sheets.

The sheet tray 130 is provided with a side guide 136 and an end guide137 as movable guides in order to cope with cut sheets P of a pluralityof sizes. The direction of the cut sheet P is turned to the transportdirection by the side guide 136.

FIG. 4 is a view showing a state of occurrence of a skew.

Although the direction of the cut sheet P is turned to the transportdirection by contact with the side guides 136 on both sides, a slightgap may be generated between the cut sheet P and the side guide 136, andthe cut sheet P may be inclined by the gap. In a case where the cutsheet P is inclined as described above, in a case where the cut sheet Pis taken out in the direction of the arrow in the drawing, theinclination may be enlarged and a skew may occur. In addition, comparinga case where the length of the cut sheet P is short as indicated by thedotted line with a case where the length of the cut sheet P is long asindicated by the solid line, even in a case where the gap between thecut sheet P and the side guide 136 is substantially the same, the cutsheet P having a short length tends to have a larger inclination. As aresult, as a general tendency, the cut sheet P having a short lengthgenerates a larger skew as compared with the cut sheet P having a longlength.

FIG. 5 is a view showing a state of occurrence of a skew in a cut sheethaving a rounded corner shape.

In addition, comparing a case where the shape of the cut sheet P is arounded corner shape as indicated by the dotted line with a case wherethe shape of the cut sheet P is a normal shape as indicated by the solidline, even in a case where the gap between the cut sheet P and the sideguide 136 is substantially the same, the cut sheet P having a roundedcorner shape tends to have a larger inclination. As a result, as ageneral tendency, as compared with the cut sheet P of a normal shape,the cut sheet P of a rounded corner shape has a larger skew.

The skew occurring in a case where the cut sheet P is taken out of thesheet tray 130 is corrected when the cut sheet P reaches theregistration roll 135, and the direction of the cut sheet P is correctedin the direction along the transport direction.

FIG. 6 is a view showing a state in which a cut sheet has reached aregistration roll.

The registration roll 135 sandwiches the cut sheet P with the backuproll 134, and feeds out the cut sheet P by rotation. The backup roll 134rotates as the registration roll 135 rotates.

In a case where the cut sheet P fed from the sheet tray 130 by the feedroller 131 reaches the registration roll 135, the leading edge thereofcollides with the registration roll 135 and a collision force isgenerated. In addition, even after the leading edge of the cut sheet Pcollides with the registration roll 135, the cut sheet P continues to bepushed toward the registration roll 135 by the feed roller 131.

The skew of the cut sheet P is corrected by the collision forcegenerated by the collision with the registration roll 135.

FIG. 7 is an explanatory view for explaining skew correction.

FIG. 7 shows a time of transport (A) in which the cut sheet P is skewedand a time of correction (B) in which the cut sheet P collides with theregistration roll 135.

The cut sheet P skewed at the time of transport (A) is directed to theregistration roll 135 while being inclined to the transport directionindicated by the arrow in FIG. 7. At the time of correction (B), theleading edge of the cut sheet P collides with the registration roll 135to generate a collision force, and a torque T is generated on the cutsheet P due to the collision force. The skew of the cut sheet P iscorrected by the torque T, and the direction of the cut sheet P iscorrected so as to approach the transport direction.

In a case where the skew occurring at the time of transport (A) issmall, the direction of the cut sheet P is aligned in the transportdirection at the time of correction (B). On the other hand, in a casewhere the skew occurring at the time of transport (A) is large, even ina case where the direction of the cut sheet P is corrected at the timeof correction (B), the inclination of the cut sheet P with respect tothe transport direction remains. In a case where the cut sheet P passesthrough the registration roll 135, there is no effect of correcting theskew, so the skew remaining after the correction is also present duringthe subsequent image formation.

FIG. 8 is an explanatory view for explaining skew correction in a narrowcut sheet.

FIG. 8 shows a time of transport (A) and a time of correction (B), in acase where the width of the cut sheet P is narrower than the width ofthe cut sheet P shown in FIG. 7.

Even in a case of the cut sheet P having a narrow width, in a case wherea skew occurs at the time of transport (A), the cut sheet P is directedto the registration roll 135 while being inclined to the transportdirection indicated by the arrow in FIG. 8. At the correction time (B),the leading edge of the cut sheet P collides with the registration roll135 to generate a collision force. However, in a case where the width ofthe cut sheet P is narrow, the torque T generated by the collision forcebecomes a small torque T. As a result, in the case of a cut sheet Phaving a narrow width, the power of correcting a skew becomes small, andthe inclination of the cut sheet P with respect to the transportdirection is likely to remain even after correction. That is, as ageneral tendency, as compared with wide cut sheets P, narrower cutsheets P have a large skew at the time of image formation.

FIG. 9 is an explanatory view for explaining skew correction in a cutsheet having a rounded corner shape.

FIG. 9 shows a time of transport (A) and a time of correction (B) of thecut sheet P having a rounded corner shape.

Even in a case of the cut sheet P of a rounded corner shape, in a casewhere a skew occurs at the time of transport (A), the cut sheet P isdirected to the registration roll 135 while being inclined to thetransport direction indicated by the arrow in FIG. 8. At the correctiontime (B), the leading edge of the cut sheet P collides with theregistration roll 135 to generate a collision force. At this time, thesubstantial width W of the cut sheet P colliding with the registrationroll 135 is narrowed by the amount by which the corner of the cut sheetP is round, and similar to the narrow cut sheet P shown in FIG. 8, thetorque T generated by the collision force becomes a small torque T. As aresult, even in the case of the cut sheet P of a rounded corner shape,the power of correcting a skew becomes small, and the inclination of thecut sheet P with respect to the transport direction is likely to remaineven after correction. That is, as a general tendency, as compared withthe cut sheet P of a normal shape, the cut sheet P of a rounded cornershape has a larger skew at the time of image formation.

The skew correction by collision between the registration rolls 135 andthe cut sheet P, described in FIGS. 7 to 9, is achieved by bending thecut sheet P at the time of collision.

FIG. 10 is a view showing bending of a cut sheet.

FIG. 10 is a side view (A) and a front view (B) showing the state of thecut sheet P whose skew is corrected by the collision with theregistration roll 135.

Even after the leading edge of the cut sheet P collides with theregistration roll 135, the feeding by the feed roller 131 continues atthe subsequent portion of the cut sheet P. Therefore, the cut sheet P istemporarily bent. The bending absorbs the difference in the direction ofthe cut sheet P which occurs on the leading edge side and the subsequentside in a case where the skew of the cut sheet P is corrected by thecollision with the registration roll 135. As a result, the skewcorrection is performed smoothly, and the direction of the cut sheet Pis corrected so as to approach the transport direction indicated by thearrow in FIG. 10.

FIG. 11 is a view showing bending in a thick cut sheet.

FIG. 11 is a side view (A) and a front view (B) showing the state ofbending in a case where the thickness of the cut sheet P is thicker thanthat of the cut sheet P shown in FIG. 10.

In a case where the thickness of the cut sheet P is large, the bendingis small even in a case where the leading edge of the cut sheet Pcollides with the registration roll 135. Therefore, in a case where thefeeding by the feed roller 131 continues at the subsequent portion,while the skew correction is insufficient, the leading edge of the cutsheet P may rush between the registration roll 135 and the backup roll134. As a result, in the case of a thick cut sheet P, the power ofcorrecting a skew becomes small, and the inclination of the cut sheet Pwith respect to the transport direction is likely to remain even aftercorrection. That is, as a general tendency, as compared with thin cutsheets P, thick cut sheets P have a large skew at the time of imageformation.

As described above, the size of the skew present at the time of imageformation varies depending on the size, shape, and the like of the cutsheet P. The strength of the influence on the size of the skew is strongin the order of size, shape and thickness.

In the image forming apparatus 100 according to the first exemplaryembodiment, information on the size, shape, and thickness of the cutsheet P is input by a user's operation.

FIG. 12 is a view showing a tray setting screen on which information oncut sheets is input.

The tray setting screen 161 is a screen displayed on the display panel160 shown in FIG. 1, and the information on the size, shape, andthickness of the cut sheet P is selectively input by the user touchingan area on the tray setting screen 161. The display panel 160 displayingthe tray setting screen 161 corresponds to an example of the input unitin the present invention.

On the tray selection field 162 of the tray setting screen 161, aselection buttons 165 for selecting a tray to which the information onthe cut sheet P is associated is arranged.

Selection buttons 166, 167 for selecting a combination of the length inthe transport direction and the width in the direction intersecting thetransport direction as the size of the cut sheet P are arranged in thesize selection field 163 of the tray setting screen 161. Further, alongwith a selection button 166 for selecting a cut sheet P having a normalshape, a selection button 167 for selecting a cut sheet P having arounded corner shape is also arranged. That is, in the size selectionfield 163, three pieces of information such as the length, width, andcorner shape of the cut sheet P are input.

A selection button 168 for selecting the basis weight generally used asan index representing the thickness of the cut paper P is arranged onthe basis weight selection field 164 of the tray setting screen 161.

By the user operating the selection buttons 165, 166, 167, 168 on thetray setting screen 161, the information on the cut sheet P is input tothe image forming apparatus 100 and stored in the control unit 180 shownin FIG. 1. Based on the information on the cut sheet P, the control unit180 selectively uses the protrusion amount 210 at the normal time (A)and the protrusion amount 230 at the countermeasure time (C) as shown inFIG. 2. The control unit 180 corresponds to an example of a protrusionamount setting unit in the present invention.

FIG. 13 is a flowchart showing control for selectively using theprotrusion amount.

In a case where the user instructs the image forming apparatus 100 toexecute a so-called job, the control shown in the flow of FIG. 13 isexecuted.

In a case where this control is started, the control unit 180 checks theinformation on the cut sheet P associated with the sheet tray 130selected by the user for image formation. The control unit 180 checksthe length of the cut sheet P (that is, the sheet length) in step S101,and in a case where the length is 7 inches or less, the skew is large.Therefore, the control unit 180 proceeds to step S105 and sets theprotrusion amount to 3 mm, for example. This protrusion amountcorresponds to the wide protrusion amount 230 at the time ofcountermeasure (C) shown in FIG. 2.

In a case where it is determined in step S101 that the length of the cutsheet P is longer than 7 inches, the control unit 180 proceeds to stepS102. The control unit 180 checks the width of the cut sheet P (that is,the sheet width) in step S102, and in a case where the width is 5 inchesor less, the skew is large. Therefore, the control unit 180 proceeds tostep S105 and sets the protrusion amount to 3 mm wide.

In a case where it is determined in step S102 that the width of the cutsheet P is wider than 5 inches, the control unit 180 proceeds to stepS103. The control unit 180 checks the shape of the cut sheet P in stepS103, and in a case where the shape is a rounded corner shape, the skewis large. Therefore, the control unit 180 proceeds to step S105 and setsthe protrusion amount to 3 mm wide.

In a case where it is determined in step S103 that the shape of the cutsheet P is a normal shape, the control unit 180 proceeds to step S104.The control unit 180 checks the basis weight of the cut sheet P in stepS104, and in a case of the cut sheet P having the basis weight of 256gsm or more, the skew is large. Therefore, the control unit 180 proceedsto step S105 and sets the protrusion amount to 3 mm wide.

In a case where it is determined in step S104 that the basis weight isless than 256 gsm, the skew is small. Therefore, the control unit 180proceeds to step S106 and sets the protrusion amount to 2 mm. Thisprotrusion amount corresponds to the narrow protrusion amount 210 at thenormal time (A) shown in FIG. 2.

Thus, in the first exemplary embodiment, selectively use of theprotrusion amount corresponding to the size of the skew is performedbased on the information on the cut sheet P. Since the protrusion amountis selectively used in accordance with the size of the skew, anappropriate protrusion amount is set even in a case where the skewoccurs.

Here, although an example in which the setting of the protrusion amountis switched only in one step has been described, the setting of theprotrusion amount may be switched in a plurality of steps. In suchmulti-step switching, as an example, control may be performed asfollows. In a case where the length of the cut sheet P is short and thewidth is narrow, the skew is large, so the protrusion amount is set to 4mm, for example. Further, in a case where the shape of the cut sheet Pis a rounded corner shape and the thickness of the cut sheet P is large,the skew is moderate, so the protrusion amount is set to 3 mm, forexample. Further, the skew is small for the other cut sheets P, so theprotrusion amount is set to 2 mm, for example.

Next, a second exemplary embodiment of the present invention will bedescribed. The second exemplary embodiment is an exemplary embodimentsimilar to the first exemplary embodiment except that the size of thecut sheet P is obtained by measurement, and therefore, the descriptionwill be focused on the difference, and the redundant description will beomitted.

FIG. 14 is a view showing a measurement mechanism of the size of a cutsheet in the second exemplary embodiment.

FIG. 14 shows the lower surface side of the sheet tray 130, and as anexample, a mechanism which measures the length of the cut sheet bymeasuring the position of the end guide 137 is shown. The measurementmechanism shown in FIG. 14 corresponds to an example of the mediummeasurement unit according to the exemplary embodiment of the presentinvention.

The end guide 137 moves in the vertical direction of FIG. 14 along aslit 301 provided on the bottom plate of the sheet tray 130. The endguide 137 is moved by the user in accordance with the length of the cutsheet stored in the sheet tray 130. A rotating portion 302 protruding tothe lower surface side of the sheet tray 130 is rotatably fixed to theend guide 137. A rotating bar 304 which rotates around a fulcrum 303passes through the rotating portion 302 of the end guide 137.

A guide rail 305 is provided on the side of the sheet tray 130, and amoving plate 306 moves along the guide rail in the vertical direction inFIG. 14. A rotating portion 307 protruding to the lower surface side ofthe sheet tray 130 is rotatably fixed to the moving plate 306. Therotating bar 304 also passes through the rotating portion 307 of themoving plate 306. The moving plate 306 is connected to the end guide 137through the rotating bar 304, and in a case where the end guide 137moves, the moving plate 306 also moves in conjunction.

A plurality of optical sensors 308 are provided at positions facing theguide rail 305. Since the optical sensor 308 has a structure in whichthe light source and the light receiving element face in the depthdirection in FIG. 14, in a case where the moving plate 306 entersbetween the light source and the light receiving element, the light isblocked and the position of the moving plate 306 is detected. In a casewhere the position of the moving plate 306 is detected, the position ofthe end guide 137 with which the moving plate 306 moves in conjunctionis also detected.

In the second exemplary embodiment, the length of the cut sheet storedin the sheet tray 130 is measured by detecting the position of the endguide 137 by using such a measurement mechanism. In the second exemplaryembodiment, the position of the side guide 136 (see FIG. 5) is alsodetected by the measurement mechanism similar to the measurementmechanism shown in FIG. 14 and the width of the cut sheet is measured.Then, based on the length and width of the cut sheet obtained by thesemeasurements, selective use of the protrusion amount according to thesize of the skew is executed as in the first exemplary embodiment.

Next, a third exemplary embodiment of the present invention will bedescribed. The third exemplary embodiment is an exemplary embodimentsimilar to the first exemplary embodiment except that the size of theskew (for example, the amount of skew) is measured, and therefore, thedescription will be focused on the difference, and the redundantdescription will be omitted.

As described above, the skew of the cut sheet P is corrected at the timeof collision with the registration roll 135, the measurement of theamount of skew is performed on the cut sheet P which has passed throughthe registration roll 135.

FIG. 15 is a view showing a measurement mechanism of a skew amount inthe third exemplary embodiment.

In the third exemplary embodiment, the side edge sensor 310 is used tomeasure the skew amount of the cut sheet P. The side edge sensor 310 isa sensor array provided between the registration roll 135 and the drivenroll 122, and optically detects the position of the edge extending alongthe transport direction for the cut sheet P transported by theregistration roll 135 upward in FIG. 15. The detection value by the sideedge sensor 310 is used to adjust the formation position of the tonerimage, or the like, but in the third exemplary embodiment, the side edgesensor 310 is also used to measure the skew amount, so an increase inthe number of parts is suppressed. The side edge sensor 310 correspondsto an example of the inclination measurement unit according to theexemplary embodiment of the present invention, and also corresponds toan example of the edge detector according to the exemplary embodiment ofthe present invention.

FIG. 16 is a view showing a method of measuring the skew amount of thecut sheet P from a detection value of the side edge sensor.

FIG. 16 shows a graph representing the time lapse of the detection valueof the side edge sensor 310, the horizontal axis of the graph shows thetime, and the vertical axis of the graph shows the position of the edgedetected by the side edge sensor.

The amount of skew is measured by obtaining a difference betweendetected positions at two time points T1, T2 separated by apredetermined specific elapsed time, which is shorter than the time forthe cut sheet P to reach the driven roll 122 from the registration roll135. In the third exemplary embodiment, unlike the first exemplaryembodiment, the protrusion amount is selectively used depending on theskew amount measured in this manner. That is, in the first exemplaryembodiment, the selective use indirectly according to the skew amountbased on the information of the cut sheet P is performed, whereas in thethird exemplary embodiment, the selective use directly according to theskew amount is performed, and the accuracy of selective use is high.

Next, a fourth exemplary embodiment of the present invention will bedescribed. The fourth exemplary embodiment is an exemplary embodimentsimilar to the third exemplary embodiment except that the method ofmeasuring the skew amount is different, and therefore, the descriptionwill be focused on the difference from the third exemplary embodiment,and the redundant description will be omitted.

FIG. 17 is a view showing a measurement mechanism of a skew amount inthe fourth exemplary embodiment.

In the fourth exemplary embodiment, two passage sensors 311, 312 fordetecting the passage of the cut sheet P are used to measure the skewamount of the cut sheet P. The passage sensors 311, 312 are reflectiontype sensors provided between the registration roll 135 and the drivenroll 122, and detect the presence or absence of the cut sheet Ptransported by the registration roll 135 upward in FIG. 17 as a binaryvalue. The two passage sensors 311, 312 correspond to an example of theinclination measurement unit according to the exemplary embodiment ofthe present invention.

FIG. 18 is a view showing a method of measuring the skew amount of thecut sheet P from a detection value of a passage sensor.

FIG. 18 shows a graph representing the time lapse of the detection valueof each of the passage sensors 311, 312, the horizontal axis of thegraph shows the time, and the vertical axis of the graph shows thepresence or absence of the cut sheet P detected by each of the passagesensors 311, 312.

The skew amount is measured by obtaining the difference in detectiontimings of the cut sheet P by the two passage sensors 311, 312. In thefourth exemplary embodiment, as in the third exemplary embodiment, theprotrusion amount is selectively used depending on the skew amountmeasured in this manner. Even in the fourth exemplary embodiment,selective use is performed directly according to the skew amount, andthe accuracy of selective use is high.

Next, a fifth exemplary embodiment of the present invention will bedescribed. The fifth exemplary embodiment is an exemplary embodimentsimilar to the first exemplary embodiment except that the shape of thecut sheet is obtained by measurement, and therefore, the descriptionwill be focused on the difference, and the redundant description will beomitted.

FIG. 19 is a view showing a measurement mechanism of the shape of a cutsheet in a fifth exemplary embodiment.

In the fifth exemplary embodiment, the side edge sensor 310 similar tothat of the third exemplary embodiment is used to measure the shape ofthe cut sheet P.

In FIG. 19, a deployment view (A) of the side edge sensor 310 and agraph (B) of detection values by the side edge sensor 310 are shown. Thehorizontal axis of the graph (B) indicates time, and the vertical axisindicates the detection position of the edge by the side edge sensor 310and the differential amount of the detection position.

The absolute value of the maximum value or the minimum value that occursin the graph representing the differential amount of the detectedposition of the edge represents the sharpness of shape of the corner,and the shape of the cut sheet P is measured by calculating the absolutevalue of the maximum value or the minimum value. In the example shown inFIG. 19, it is measured that the shape of the cut sheet P is a normalshape. The calculation of the absolute value of the maximum value or theminimum value is performed by, for example, the control unit 180. Thecombination of the side edge sensor 310 and the control unit 180 in thefifth exemplary embodiment corresponds to an example of the mediummeasurement unit in the present invention.

FIG. 20 is a view showing a measurement example of a cut sheet having arounded corner shape in the fifth exemplary embodiment.

In FIG. 20, a deployment view (A) of the side edge sensor 310 and agraph (B) of detection values by the side edge sensor 310 are shown.

In the case of the cut sheet P of a rounded corner shape, since thedetection position of the edge by the side edge sensor 310 changessmoothly, the absolute value of the maximum value or the minimum valueoccurring in the graph representing the differential amount of thedetection position of the edge is small. That is, by calculating theabsolute value of the maximum value or the minimum value of such adifferential amount, it is measured that the cut sheet P has a roundedcorner shape.

In the fifth exemplary embodiment, the information on the shape of thecut sheet P obtained by such measurement is used to selectively use theprotrusion amount, as in the first exemplary embodiment.

Next, a sixth exemplary embodiment of the present invention will bedescribed. The sixth exemplary embodiment is an exemplary embodimentsimilar to the first exemplary embodiment except that the thickness ofthe cut sheet is obtained by measurement, and therefore, the descriptionwill be focused on the difference, and the redundant description will beomitted.

FIG. 21 is a view showing a measurement mechanism of the thickness of acut sheet in a sixth exemplary embodiment.

In the sixth exemplary embodiment, the drive current value at the feedroll 131 is used to measure the thickness of the cut sheet.

As shown in the state diagram (A) of FIG. 21, in a case where theleading edge of the cut sheet P reaches the position where theregistration roll 135 and the backup roll 134 contact, the leading edgeof the cut sheet P is pressed down by the registration roll 135 and thebackup roll 134. As a result, in the graph (B) representing the drivecurrent value, a peak of the drive current value occurs. In the case ofa thin cut sheet P, since the cut sheet P is largely bent, the peak ofthe drive current value is small. On the other hand, as shown in thestate diagram (C), in a case where the thick cut sheet P is pressed downby the registration roll 135 and the backup roll 134, the bending of thecut sheet P is small. Therefore, a large peak occurs in the graph (D)representing the drive current value. As described above, the thicknessof the cut sheet P is measured by obtaining the peak occurring in thedrive current value at the feed roll 131. The peak occurring in thedrive current value is calculated by, for example, the control unit 180.The combination of the feed roll 131 and the control unit 180 in thesixth exemplary embodiment corresponds to an example of a mediummeasurement unit in the present invention.

In the sixth exemplary embodiment, the thickness of the cut sheet Pobtained by such measurement is used to selectively use the protrusionamount, as in the first exemplary embodiment.

In the above description, a color printer is shown as an example of theimage forming apparatus according to the exemplary embodiment of thepresent invention, but the image forming apparatus according to theexemplary embodiment of the present invention may be a monochromeprinter, a copier or a multifunction peripheral.

In the above description, an image engine that forms a toner image by anelectrophotographic method is shown as an example of the image formingdevice according to the exemplary embodiment of the present invention.However, the image forming device referred to in the present inventionmay form an image, for example, by inkjet.

In addition, the present invention has been made for the purpose ofaddressing the problems described in the section “Technical Problem”,but the configuration of the present invention does not prevent thediversion to other purposes in the form not to address the problem, anda form in which the configuration of the present invention is divertedis also an exemplary embodiment of the present invention.

The foregoing description of the exemplary embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

What is claimed is:
 1. An image forming apparatus comprising: atransport unit that transports a recording medium along a transport pathto a formation area in which an image is formed on the recording medium;an image forming unit that fours the image on the recording medium inthe formation area; and a protrusion amount setting unit that sets aprotrusion amount of the image protruding from the recording medium to afirst protrusion amount in a first case, and sets the protrusion amountto a second protrusion amount larger than the first protrusion amount ina second case where the recording medium is inclined to a transportdirection more than the first case, wherein the protrusion amountsetting unit acquires information on the recording medium, sets theprotrusion amount to the first protrusion amount, in a case where theacquired information indicates a recording medium corresponding to thefirst case, and sets the protrusion amount to the second protrusionamount, in a case where the acquired information indicates a recordingmedium corresponding to the second case, and wherein the protrusionamount setting unit acquires a shape of a corner of the recording mediumas the information on the recording medium, and sets the protrusionamount to the second protrusion amount, in the second case where thecorner is more blunt than the first case.
 2. The image forming apparatusaccording to claim 1, further comprising: a medium measurement unit thatmeasures a shape of a corner of the recording medium to obtain theinformation, wherein the protrusion amount setting unit acquires theinformation from the medium measurement unit.
 3. An image formingapparatus comprising: a transport unit that transports a recordingmedium along a transport path to a formation area in which an image isformed on the recording medium; an image forming unit that forms theimage on the recording medium in the formation area; and a protrusionamount setting unit that sets a protrusion amount of the imageprotruding from the recording medium to a first protrusion amount in afirst case, and sets the protrusion amount to a second protrusion amountlarger than the first protrusion amount in a second case where therecording medium is inclined to a transport direction more than thefirst case, the image forming apparatus further comprising: aninclination measurement unit that measures an inclination of therecording medium with respect to the transport direction, wherein theprotrusion amount setting unit sets the protrusion amount to the firstprotrusion amount, in a case where the inclination measured by theinclination measurement unit corresponds to the first case, and sets theprotrusion amount to the second protrusion amount, in a case where themeasured inclination corresponds to the second case, and the imageforming apparatus further comprising: an edge detection unit thatdetects a position of an edge extending along the transport direction,among edges of the recording medium, wherein the inclination measurementunit measures the inclination using the edge detection unit.